Cellulose is the structural component of the primary cell wall of green plants, many forms of algae and the oomycetes, and is the most common organic compound on the earth. Cellulose is a polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units. The basic units of cellulose are nanocellulose fibrils that are formed of an in intermixing of areas of disordered structural regions and crystalline structural regions. Isolated crystalline structural regions, or nanocrystalline cellulose (NCC), are very strong and have a strength to weight ratio that is better than stainless steel.
Nanocrystalline cellulose is lightweight, conducts electricity, is as strong as Kevlar, is not harmful to humans, and is available from plant sources. However, a number of technical bottlenecks hinder a cost effective production of NCC. Production of NCC requires expensive starting materials, for example, bleached pulp or microcrystalline cellulose, to produce high quality NCC. The crystallinity of most starting material is also below 55%. In addition, since concentrated mineral acids are used to hydrolyze non-crystalline cellulose to soluble sugars, more than half of the initial materials are wasted in the production process. The huge consumptions of inorganic acid and subsequent neutralization agents represent another major economical bottleneck in NCC production. Cost factors have significantly limited commercial production and therefore applications of NCC, and there remains a need for improved processes for the production of high-quality NCC.
There may be many future applications for NCC. Because of its strength, NCC may be usable as a replacement for metal and plastic parts and could make non-organic plastics obsolete. Because of the unique properties of NCC, promising commercial applications may be developed in many industrial sectors including paints, coatings, textiles, polymer composites and cosmetics. In addition, NCC may also be applicable to biological uses as well. For example, many different tissues may be repaired by grafting, including: skin, bone, nerve, tendon, blood vessel, fat and cornea tissues. Grafting refers to a surgical procedure to move tissue from one site to another on the body, or from one body to another, or to repair tissue with synthetic substitutes. As an example, skin grafting is often used to treat skin loss due to wounds, burns, infections or surgeries. In the case of damaged skin, the damaged portion is removed, and new skin is grafted in its place. Skin grafting can reduce the course of treatment and hospitalization needed, and can also improve function and appearance. Vascular grafting is the use of transplanted or prosthetic blood vessels to repair damaged, or clogged blood vessels in surgical procedures.
Autologous vessel grafts, or those that are taken from other vascular parts of the patient, have typically been the only replacement grafts that have great long-term success on implantation. However, the body has only a limited supply of usable vessels for grafting, especially when one needs multiple bypasses. The two most common synthetic vascular graft materials; polytetrafluoroethylene (PTFE) and polyethylene terephthalate (PET), are generally only suitable for grafts having diameters larger than about 6 mm. Synthetic materials for the replacement of small-diameter vascular grafts (e.g. coronary, renal, and carotid) generally do not have suitable biological and mechanical properties.
Biological and mechanical compliance are the two most critical properties required for artificial vascular grafts, and this typically applies to other tissue grafts as well. The material should be biocompatible and should possess mechanical properties that mimic those of the native tissue. For vasculature, synthetic grafts should have both strength and elasticity to withstand the pulsatile pressures of the physiological environment. A common limitation of existing materials is the failure to provide long-term functionality, as typical vascular grafts either, became blocked with blood clots due to biological incompatibility, or disintegrate due to lack of mechanical strength.
There remains a need for the development of improved synthetic tissues for tissue grafts, and in particular for vascular grafts, such as small diameter grafts. Synthetic materials, in particular for vascular grafts, should have a strength and elasticity comparable to that of the tissue being repaired, and should have a biocompatibility with the tissue being repaired.